John McTernan is a commentator and political strategist who works internationally. He was Political Secretary to Tony Blair and most recently was the Director of Communications for Australian Prime Minister Julia Gillard.

What you will hear after the Oldham East and Saddleworth by-election result

Cameron canvasses votes in Oldham East and Saddleworth (Photo: Reuters)

Polls put Labour on track to win the by-election in Oldham East and Saddleworth. This, despite the weather and agreed line (from Labour and the Lib Dems) that it's too close to call. What, though, will the lasting meaning of this by-election be? Let's look at the possible scenarios, in ascending order of likelihood.

1. The Impossible

The Tories gain the seat. Eric Pickles claims the credit for a lo-fi, cheap as chips, under the radar victory. The 1922 demand an end to the Coalition, celebrate Cameron's strategic genius and call for a General Election. Huhne replaces Clegg. The Labour Party plan for a leadership election after a crushing General Election defeat in May.

2.The Highly Unlikely

The Lib Dems gain the seat. Nick Clegg celebrates his own strategic genius. Simon Hughes and Tim Farron celebrate theirs. The 1922 demand an end to the Coalition. Cameron is pleased that Clegg is pleased. Labour say they never expected to win. Unique circumstances. Century-long tradition of liberalism locally. The Shadow Cabinet pledge undying loyalty to Ed and a renewed commitment to winning in Scotland, Wales and the English local elections while filling their diaries with fundraising dinners in constituencies across the country.

3. The Unlikely

Labour win narrowly. Nick Clegg claims a moral victory. Says he never expected to win. Unique circumstances. Pickles says austerity campaign was vindicated. The 1922 demand an end to the Coalition. Cameron says Ed is fatally wounded, Labour should have romped home. Labour say one vote is enough. Never took the seat for granted. Unique circumstances. Long haul. A journey of 1000 miles starts with one pace. Half a dozen members of the Shadow Cabinet individually approach the Fabian Society suggesting they draft a thoughtful, philosophical pamphlet on the Forward March of Labour.

4. The Highly Likely

Labour win handsomely. Chris Huhne fills his diary with constituency fundraisers and drafts a pamphlet on green-red politics. The 1922 demand an end to the coalition. Baroness Warsi blames the Labour Party. Cameron tells his team it's a great result. It ties the Lib Dems deeper into the coalition and makes Labour complacent. Tim Montgomerie produces a table that shows the swing to Labour is exactly what Neil Kinnock was receiving at this stage in his leadership of the Labour Party.

This is, in the end, all about Labour. And more precisely, all about Ed Miliband. He needs a strong result because Oldham East and Saddleworth is a seat where Labour shouldn't need to break sweat. Phil Woolas held the seat when Labour were a bare six points ahead of the Lib Dems nationally; with the margin now closer to 36 points this should fall into his lap. A less than stunning victory will lead to a string of articles telling him to be bolder and define himself or he won't win the trust of the public – according to the prejudices of the commentator. A stunning victory will lead to a string of articles urging him to be bolder and define himself or he'll lose the trust of the public.

But most importantly Miliband needs to be able to pull off the trick of making the result – whatever it is – seem significant, while knowing that it isn't. The turning point by-elections are few and far between. Darlington, which saved Michael Foot's leadership. Eastbourne, which torpedoed Margaret Thatcher's. The rest vanish like snow off a dyke.